How to Use Monolog to Write Logs
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How to Use Monolog to Write Logs
Monolog is a logging library for PHP used by Symfony. It is inspired by the Python LogBook library.
Usage
To log a message simply get the logger service from the container in
your controller:
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public function indexAction()
{
$logger = $this->get('logger');
$logger->info('I just got the logger');
$logger->error('An error occurred');
// ...
}The logger service has different methods for different logging levels.
See LoggerInterface for details
on which methods are available.
Handlers and Channels: Writing Logs to different Locations
In Monolog each logger defines a logging channel, which organizes your log messages into different "categories". Then, each channel has a stack of handlers to write the logs (the handlers can be shared).
Tip
When injecting the logger in a service you can use a custom channel control which "channel" the logger will log to.
The basic handler is the StreamHandler which writes logs in a stream
(by default in the app/logs/prod.log in the prod environment and
app/logs/dev.log in the dev environment).
Monolog comes also with a powerful built-in handler for the logging in
prod environment: FingersCrossedHandler. It allows you to store the
messages in a buffer and to log them only if a message reaches the
action level (error in the configuration provided in the Symfony Standard
Edition) by forwarding the messages to another handler.
Using several Handlers
The logger uses a stack of handlers which are called successively. This allows you to log the messages in several ways easily.
- YAML
- XML
- PHP
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# app/config/config.yml
monolog:
handlers:
applog:
type: stream
path: /var/log/symfony.log
level: error
main:
type: fingers_crossed
action_level: warning
handler: file
file:
type: stream
level: debug
syslog:
type: syslog
level: errorThe above configuration defines a stack of handlers which will be called in the order they are defined.
Tip
The handler named "file" will not be included in the stack itself as
it is used as a nested handler of the fingers_crossed handler.
Note
If you want to change the config of MonologBundle in another config file you need to redefine the whole stack. It cannot be merged because the order matters and a merge does not allow to control the order.
Changing the Formatter
The handler uses a Formatter to format the record before logging
it. All Monolog handlers use an instance of
Monolog\Formatter\LineFormatter by default but you can replace it
easily. Your formatter must implement
Monolog\Formatter\FormatterInterface.
- YAML
- XML
- PHP
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# app/config/config.yml
services:
my_formatter:
class: Monolog\Formatter\JsonFormatter
monolog:
handlers:
file:
type: stream
level: debug
formatter: my_formatterHow to Rotate your Log Files
Over time, log files can grow to be huge, both while developing and on production. One best-practice solution is to use a tool like the logrotate Linux command to rotate log files before they become too large.
Another option is to have Monolog rotate the files for you by using the
rotating_file handler. This handler creates a new log file every day
and can also remove old files automatically. To use it, just set the type
option of your handler to rotating_file:
- YAML
- XML
- PHP
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# app/config/config_dev.yml
monolog:
handlers:
main:
type: rotating_file
path: '%kernel.logs_dir%/%kernel.environment%.log'
level: debug
# max number of log files to keep
# defaults to zero, which means infinite files
max_files: 10How to Disable Microseconds Precision
2.11
The use_microseconds option was introduced in MonologBundle 2.11.
Setting the parameter use_microseconds to false forces the logger to reduce
the precision in the datetime field of the log messages from microsecond to second,
avoiding a call to the microtime(true) function and the subsequent parsing.
Disabling the use of microseconds can provide a small performance gain speeding up the
log generation. This is recommended for systems that generate a large number of log events.
- YAML
- XML
- PHP
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# app/config/config.yml
monolog:
use_microseconds: false
handlers:
applog:
type: stream
path: /var/log/symfony.log
level: errorAdding some extra Data in the Log Messages
Monolog allows you to process the record before logging it to add some extra data. A processor can be applied for the whole handler stack or only for a specific handler.
A processor is simply a callable receiving the record as its first argument.
Processors are configured using the monolog.processor DIC tag. See the
reference about it.
Adding a Session/Request Token
Sometimes it is hard to tell which entries in the log belong to which session and/or request. The following example will add a unique token for each request using a processor.
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namespace AppBundle;
use Symfony\Component\HttpFoundation\Session\Session;
class SessionRequestProcessor
{
private $session;
private $token;
public function __construct(Session $session)
{
$this->session = $session;
}
public function processRecord(array $record)
{
if (null === $this->token) {
try {
$this->token = substr($this->session->getId(), 0, 8);
} catch (\RuntimeException $e) {
$this->token = '????????';
}
$this->token .= '-' . substr(uniqid(), -8);
}
$record['extra']['token'] = $this->token;
return $record;
}
}- YAML
- XML
- PHP
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# app/config/config.yml
services:
monolog.formatter.session_request:
class: Monolog\Formatter\LineFormatter
arguments:
- "[%%datetime%%] [%%extra.token%%] %%channel%%.%%level_name%%: %%message%% %%context%% %%extra%%\n"
monolog.processor.session_request:
class: AppBundle\SessionRequestProcessor
arguments: ['@session']
tags:
- { name: monolog.processor, method: processRecord }
monolog:
handlers:
main:
type: stream
path: '%kernel.logs_dir%/%kernel.environment%.log'
level: debug
formatter: monolog.formatter.session_requestNote
If you use several handlers, you can also register a processor at the handler level or at the channel level instead of registering it globally (see the following sections).
Registering Processors per Handler
You can register a processor per handler using the handler option of
the monolog.processor tag:
- YAML
- XML
- PHP
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# app/config/config.yml
services:
monolog.processor.session_request:
class: AppBundle\SessionRequestProcessor
arguments: ['@session']
tags:
- { name: monolog.processor, method: processRecord, handler: main }Registering Processors per Channel
You can register a processor per channel using the channel option of
the monolog.processor tag:
- YAML
- XML
- PHP
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# app/config/config.yml
services:
monolog.processor.session_request:
class: AppBundle\SessionRequestProcessor
arguments: ['@session']
tags:
- { name: monolog.processor, method: processRecord, channel: main }
